That’s a great question and poser for most when starting out on their 3d journey.
You can just sketch out a design, it doesn’t have to be perfect. As long as you have something to start from, often the hardest part in 3d is where/how to start your model.
You can do it free hand with pencil and paper, or like I expect with the Press Start reference images, Photoshop, Krita or similar was probably used.
There are loads of places to get reference from, Unsplash, Pixabay, Pinterest even ArtStation, searching online will give you plenty of ideas and reference.
And you don’t just need one reference, you can gather lots of reference images on your subject and take inspiration from each one and come up with something totally unique.
For example: with a console like Press Start, you could find reference of your favourite console, could even be PS or Xbox and take a bite out of it..
add/change it up with reference from other things that inspire you..
Your favourite TV show, Movie, Video Game, whatever you like.
